Leukocyte accumulation is the hallmark of inflammatory renal diseases. TNF, a potent cytokine that regulates leukocyte trafficking, is essential for the development of glomerulonephritis (GN) in animal models. The biological activities of TNF are mediated by two functionally distinct TNFRs, TNFR1 and TNFR2. We have shown that TNFR2 is critical for GN. TNFR2 deficient mice were completely protected from antibody- mediated nephrotoxic nephritis that was associated with decreased renal leukocyte accumulation and glomerular complement deposition. Furthermore, TNFR2 on intrinsic parenchymal cells but not circulating leukocytes was essential for GN. Notably, TNFR2 was induced on glomerular endothelium of nephritic kidneys. In contrast, a deficiency in TNFR1 resulted in an enhanced immune response and renal T cell accumulation resulting in GN. Thus TNFRs play differential roles in GN. The major objective of this proposal is to identify the intrinsic cell type and mechanisms responsible for TNFR2 dependent leukocyte accumulation and glomerular damage. Aim I will address the hypothesis that TNFR2 engagement on endothelial cells induces a transcriptional program required for leukocyte recruitment and subsequent glomerular injury. The endothelial adhesion receptor dependent signaling mechanisms required for leukocyte transmigration remain enigmatic. Our preliminary data demonstrates that TNF-induced leukocyte transmigration is dependent on DOCK4, a recently identified member of the COM family of guanine exchange factors for small GTPases that we show is highly expressed on cultured endothelial cells and glomerular endothelium. Aim II will test the hypothesis that endothelial adhesion receptor signaling to DOCK4 modulates leukocyte transmigration and glomerular damage. These aims will exploit a) established mouse models of antibody induced GN, and antibody and TNF-induced leukocyte recruitment that are amenable to intravital microscopy, b) transcriptional profiling of nephritic kidneys and in vitro leukocyte transmigration assays under physiological flow conditions, c) transgenic mice with inducible expression of TNFR2 only in the endothelium, and mice lacking DOCK4 specifically in the endothelial lineage. Completion of the aims will increase our understanding of endothelial dependent mechanisms of inflammation mediated glomerular injury that could aid in the development of new therapeutic strategies for the treatment of GN.